#include <stack>
class Solution
{
public:
    void push(int node) {
        stack1.push(node);
    }

    int pop() {
        if (!stack2.empty())
        {
            auto t = stack2.top();
            stack2.pop();

            return t;
        }

        while (!stack1.empty())
        {
            stack2.push(stack1.top());
            stack1.pop();
        }

        auto t = stack2.top();
        stack2.pop();

        return t;
    }

private:
    stack<int> stack1;
    stack<int> stack2;
};